1. Field of the Invention
The present invention relates to a liquid crystal driving apparatus and is more particularly directed to the development of a novel arrangement of a liquid crystal driver with which the number of liquid crystal dots available for diplay can be increased in a display panel composed of a liquid crystal dot matrix.
2. Description of the Prior Art
A liquid crystal dot matrix display is well known in the art. For example, a square display panel is formed of a liquid crystal dot matrix. According to the prior art, such a square display panel is formed and driven in the following manner:
A first signal line pattern and a second signal line pattern are formed with a liquid crystal being sandwiched in between the two signal line patterns. For example, the first signal line pattern is formed on the front surface of the liquid crystal by arranging a plurality of signal lines at regular intervals in one direction, for example, lengthwise. The second signal line pattern is formed on the back surface of the liquid crystal by arranging a plurality of signal lines at regular intervals in the direction intersecting the first signal lines at right angles, for example, widthwise. Liquid crystal dots are formed at the points where the first signal line pattern on the front surface and the second signal line pattern on the back surface intersect each other.
To selectively drive the liquid crystal dots for display, time division driving signals and selection driving signals are used. To the signal lines on one of the two surfaces there are applied time division driving signals of a definite waveform regardless of the display data to be displayed on the display panel. Applied to the signal lines on the other surface are selection driving signals corresponding to the data to be displayed. The selection driving signals are supplied in synchrony with the time division driving signals. The liquid crystal dots are driven for display by the potential difference between the two signals.
FIG. 1 shows an example of the above mentioned type of square liquid crystal display panel.
The example shown in FIG. 1 is a square liquid crystal display panel formed by an 8 (lengthwise).times.8 (widthwise) dot matrix which is driven for display by a liquid crystal display driving circuit having a driving capacity of 1/4 duty.
In FIG. 1, the signal line pattern formed on the front surface of liquid crystal is indicated by solid lines and the signal line pattern on the back surface by broken lines. Marks ".circle." indicate intersections of the front pattern and the back pattern where liquid crystal dots are formed.
The back pattern includes eight signal lines, SY1 through SY8, extending in the direction of Y. Time division signals TS1-TS4 are supplied to the signal lines SY1-SY4 from a liquid crystal display driving circuit (not shown). The square area enclosed by a chain-dotted line and indicated by P is the display screen area of the panel. At the outside of the display screen area P, the signal lines SY1 and SY5, SY2 and SY6, SY3 and SY7, SY4 and SY8 are connected by signal lines S1, S2, S3 and S4 respectively. Therefore, signals TS1-TS4 are applied also to the signal lines SY5-SY8 through liner S1-S4.
The front pattern includes sixteen signal lines, SX1 through SX16, extending in the direction of X. Selection driving signals SS1-SS16 are supplied to these signal lines SX1-SX16 from the liquid crystal display driving circuit.
The manner of driving of the above square liquid crystal display panel will be described by way of example by reffering to the signal waveforms shown in FIG. 2.
FIG. 2A shows exemplary waveforms of time division driving signals TS1-TS4 according to the four level equal division method. As an example, description is made of such a case where only two liquid crystal dots D (1, 1) and D (2, 2) are selected to be lit by means of the signals TS1-TS4. As seen in FIG. 1, the liquid crystal dot D (1, 1) is at the intersection of X1-row and Y1-line on the display panel. Namely, it is a liquid crystal dot formed by the signal lines SX1 and SY1 with liquid crystal therebetween. The liquid crystal dot D (2, 2) is at the intersection of X2-row and Y2-line and formed by signal lines SX2 and SY2 with liquid crystal therebetween.
FIG. 2B shows selection driving signals SS1 and SS2 used to select and light the liquid crystal dots D (1, 1) and D (2, 2). The liquid crystal dot lights only when the potential difference .DELTA.V between the signal line on the front surface of the liquid crystal and the signal line on the back surface thereof reaches a determined value .DELTA.Vo.
FIG. 2C shows the waveforms of signals DS1, DS2 and DS3 formed by the potential difference between signal lines TS1 and SS1 at the liquid crystal dot D (1, 1), by the potential difference between signal lines TS2 and SS2 at the liquid crystal dot D (2, 2) and by the potential difference between signal lines TS2 and SS1 at D (2, 1) where X1-row and Y2-line intersect each other. The potential differences at D (1, 1) and at D (2, 2) are sufficiently large enough to reach the dot lighting potential difference .DELTA.Vo. But, at the dot D (2, 1), the potential difference .DELTA.V does not reach the lighting potential difference .DELTA.Vo. Therefore, only the liquid crystal dots D (1, 1) and D (2, 2) light on and the dot D (2, 1) can not light on. In this manner, the liquid crystal dots are driven for display.
When the above example of a liquid crystal display panel is driven for display with a driving capacity of 1/4 duty in the manner described above, there are a limited number of dots which can be driven for display. For such a liquid crystal display panel having a driving capacity of 1/4 duty, the number of liquid crystal dots which can be selected for display by selection driving signals is limited to four. The maximum number of liquid crystal dots which can be driven for display with respect to direction X for selection driving is only eight as seen from FIG. 1A. The reason for this is that in order to drive more than eight liquid crystal dots for display in the selection driving direction (X-direction) it is necessary to supply one more kind of selection driving signal to every row on the panel in the selection driving direction. In the signal line patterns of the prior art, it has been impossible to provide such signal lines for supplying one more selection driving signal.
For example, if four dots are added to the display panel having a driving capacity of 1/4 duty in the selection driving direction (X-direction) and twelve dots in total are arranged in the direction of X as shown in FIG. 1B, then additional signal lines should be provided to supply the necessary selection driving signals for selectively driving the added four dots (see area (A) in FIG. 1B). Wiring of such additional signal lines is a difficult problem in this case. On might think that these additional signal lines can be laid making use of the space between. However, the space between dots is predetermined by certain factors. Among these factors is the requirement that the space should be sufficiently large enough to prevent two neighbouring dots from interferring with each other. Therefore, if an additional signal line is laid passing through the space between dots, then dots around the added signal line may be affected by the selection driving signal supplied through the signal line. for example, if an additional signal line J is laid between two lines Y8 and Y9 to supply a selection driving signal to dots D (5, 5)-D (8, 5) in X5-row as shown in FIG. 1B, then dots near the signal line J such as dots D (9, 6) and D (9, 7) may be affected by the signal transmitted through the signal line J. As another example, if a signal line K is additionally laid between two rows X4 and X5 as shown also in FIG. 1B, then the signal line K intersects the signal lines SY1-SY4 laid on the back surface of the liquid crystal and undesirable liquid crystal dots are formed at these intersections. In this case, not four but eight liquid crystal dots will be driven by one selection driving signal.
As can be readily understood from the foregoing, the signal line patterns according to the prior art have a particular limitation in the number of dots. Even if the number of dots is increased by additionally providing several dots such as D (5, 5)-D (8, 5) in a conventional liquid crystal display panel, it is impossible to suitably supply the necessary selection driving signal to those dots.
In case of the conventional signal line patterns, the number of liquid crystal dots which can be driven for display in the selection driving direction is determined by the driving duty of the liquid crystal display driving circuit then used. Accordingly, when a square display panel is to be made, the size of liquid crystal dot matrix, i.e., the number of dots available for display, is limited by the number of dots which can be driven for display in the selection driving direction (X-direction). For instance, in case of the square display panel having a driving capacity of 1/4 duty shown in FIG. 1, the number of dots in the selection driving direction (X-direction) is eight at maximum. Therefore, the number of dots in the time division driving direction (Y-direction) is determined directly by it to also be a maximum of eight. consequently, the maximum number of dots available for display is limited to 8.times.8 dots in total. It was impossible to form a square display panel comprising dots a matrix of larger than 8.times.8 according to the prior art.